Electromagnetic friction apparatus



Dec. 1942- H. w. PHAIR ELECTROMAGNETIC FRICTION APPARATUS Filed May 22, I940 INVENTOR Harry ill km) ATTORNEYS is much lower than at low speeds.

Patented Dec..8, 1942' L UNITED STATES PATENT OFFICE) ELEti'lROMAGNETIO FBICTIOH Barry W. Phair, y dlnirst, N. .I., assignor to Empire Electric Brake Corporation, a corporation of Delaware Application May 22, 1940', Serial No. 336,603

12 Claims.

va force is imposed on the magnet tending to move it in the direction of movement of the armature. The force thus imposed on the electromagnet may be derived for useful work through any suitable mechanism, such as a lever on which the electromagnet is mounted.

In such apparatus, using an armature composed of ordinary magnetic material, such, for

example, as ordinary iron or steel, the force derived at any given degree of energization of the electromagnet varies inversely, and to a considerable extent, with the speed at which the armature moves relatively to the electromagnet. Such variations in the derived force at various relative speeds of the armature to the electromagnet is decidedly objectionable. For example, if the apparatus is employed as a brake operating mechanism in an electromagnetic brake, in which the armature rotates with the wheel of the. vehicle or otherm'oving part to be braked, the braking effort which the apparatus is able to produce varies inversely and to a considerable extent with the speed of the wheel or other moving part. At high speeds, therefore, the braking effort for a given degree of magnet energizatio I have discovered that this objectionable characteristic of electromagnetic apparatus of the character referred to above is due to eddy currents induced in the armature as it moves relatively to the electromagnet when the latter is energized. These eddy currents create amag- -netic flux in the armature which opposes the flux produced by the electromagnet. The more rapidly the armature moves relatively to the electromagnet, the stronger are the eddy currents produced therein, and the greater is the opposition of the flux produced by the eddy currents to the flux produced by the electromagnet. Consequently, the higher the speed of the armature and the armature for any given degree for electromagnet energizatlon.

I have further found that if the armaturemoving-relatively' to the electromagnet is composed of a magnetic material such as iron containing a substantial proportion of a material such as silicon which inhibits the occurrence of eddy currents,.it is possible to derive a substantially constant force from the apparatus, at any ven degree of electromagnet energization, over aconsiderable range of speed of the armature relatively to the electromagnet. It is understood, of course, that in stating that the derived force may be made substantially constant" over aconsiderable range of speed, I do not mean the derived force will be absolutely constant. On the contrary, some variation-in the derived force will inevitably occur with variations in speed. The expression ,substantially constant" as used herein and in the appended claims is intended to mean that, in any given apparatus, the derived force is suiiiciently constant so that such force variations as do occur atdifferent speeds of the armature relatively to the electromagnet are within the tolerable range of. force variations for that particular apparatus.

' Based on the foregoing discoveries, my invention contemplates the improvement, in electromagnetic apparatus of the character referred to above, which comprisesemploying asthe armature a metallic member composed largely of iron and containing silicon in suflicientamount so that the force derite'd at a given degree-of energization of the electromagnet is substantially -constant over a considerable range of speed of the armature relatively to the electromagnet. In general a substantial amount up'to about 10% by weight of silicon isemployed in the armature to obtain the desired results. Armature's composed of an alloy of silicon with iron containving about 3% to about 8% by-weight. of the silicon have been. employed with considerable,

SUCCESS.

comprises an armature, which advantageously is a relatively thin, generally disc-shaped member mounted for rotation ,about its axis, an electromagnetmounted with its pole pieces normally in light-pressure contact with the armature, means relatively to the electromagnet, the less is the magnetic attraction between. the electromagnet the force derived at a given g f e of ene g fir for controllably energizing the electromagnet with an electric current, and means for moving the farmature relatively to the electromagnet, the armature being composed largely of iron andv containing silicon in suflicient' amount so that arm 2| short arm 2| carriesa brake-actuating pin 23 The armature may be composed wholly of an iron alloy containing silicon in a substantial .amountup'to about by weight, advantageously from about 3% to 8% by weight, or it may be a composite structure having a surface portion composed of a relatively hard,,'wear-re sistant metallic composition (such as a casehardened ferrous composition) adapted to engage with the electromagnet, and an underlying portion composed largely of iron 'and containing a suitable amount, as indicated above, -of silicon.

Electromagnetic apparatus of the character era'ted' brake embodying the invention;

Fig. 21s a cross section of the brake shown in Fig. '1, taken substantially along the line 2-2 of Fig. 1;

Fig. 3 is a plan view on a reduced scale showing the mechanical structure of an armature plate of the type employed in .the brake "shown in Figs. 1 and 2; and

Fig.4 is a fragmentary cross section through a modified form of armature plate.

The brake shown in the drawing comprises a backing plate. It on which are mounted a pair' of anchors ll. Brake shoes l2 carryinga suitable brake lining-13 are mounted on and car-' ried by the anchors Ill The brake shoes l2 are connected together at their lower ends, ap-

anchors, by suitable adjusting means It and a .lpring II. The brake shoes are provided .with

the usual hold-down means It," for holding than against the backing plate; and the usual eccentric adjustment l1, and the eccentric adj iuatmait it.

Mounted on the backing'plate is a pivot pin 'II on which a lever 2| is 'pivotally mounted. The lever "is provided with a bifurcated short and a long arm 22. The bifurcated on which is mounted. a rolier,,bearing- 24 enamine with the ends of the brake shoes l2 betweenthe anchorsll The long arm 22'of the-lever carries an annular electromagnet 2! having an inner pole piece 2| and an outer pole piece 21. A suitable annular electromagnet coil is located within the electromagnet, and wires 25a through which elecmally held out of engagement with the brake proximately diametrically opposite from the 'trlcal energy is supplied to the electromagnet coil run from the magnet up the lever 20 and are taken out through the backing plate in at a suitable point. The wires 25a are connected to a; battery B or other suitable source or current in series with a rheostat R or other suitable' means forcontrolling the value of the current supplied to, the electromagnet.

A brake drum 28 is arranged for rotation with the wheel of the vehicle or other moving part to be braked, and is positioned with its' drum surface concentric with and close to the lining II of the brake shoes l2. An armature plate. 29 in the form of a relatively thin, an-

nular member is mounted fin the brake drum 28 against bosses ill by'means of bolts 3| engaging in threaded holes 32 formed in the arm'ation of the electromagnet is substantially constant ovra considerable range of speed of the armature relatively to the electromagnet.

brake drum) and the shaft on which such part is mounted may extend through the central opening 33 of the brake drum, through the corresponding central opening 34 ofthe armature plate, and, if necessary, through .an aligned opening Illa. inithe backing plate.

The electromagnet 25 mounted on the long arm 22 of the lever is normallyheld in lightpressure contact with the armature 29 by means of a spring 35: The mounting means forthe magnet enabling this light-pressure contact to be maintained-even though the armature plate may wobbl slightly or otherwise run out of true, comprises a sleeve 36 closed at one end and mounted within the sleeve 36. The magnet mounting pin extends into the central pole or core of the magnet to a point closely adjacent the working face thereof. The spring 35 is mounted to press at one end against the closed endof the sleeve 36, and against'the magnet mounting pin 3-! at the other end, so as to press the magnet supported by the pin lightly against the armature plate 29.

The apparatus described above operates as follows: With the backing plate and brake shoes carried thereby held stationary on some 'rigid support (such as a frame member of a vehicle) and with the rotating brake drum and armature rotating so that the armature moves relatively to the electromagnet, the brake shoes are nordrum by means of a retracting spring 38. Upon energizing the electromagnet by operating the rheostat R to pass a current of suitable controlled value through the electromagnet coil, the magnet is attracted to the rotating armature with a force that is roughly proportional through the lever 20 and is applied by the short" arm of the lever to the end of one of the shoes l2, depending upon the directionof rotation oiv the armature, and the shoe so acted upon is thereby expanded outwardly into braking engagement with the drum 28. By contrcllably varying the degree to which the electromagnet 'is energized, that is, by controllably varying the amount of current supplied to the electromag net coil, the friction between the rotating armature and the electromagnet is correspondingly controllably varied. In this manner the force applied to the ends of the brake shoes, and the braking effort exerted by the latter, are easilycontrolled.

If the armature'plate is composed of an ordinary magnetic material, such as an ordinary iron or steel, theforce with which the brake shoe is expanded at,'any given degree of energization of the electromagnet (i. e. at any given current value supplied to the electromagnet coil) varies inversely with the speed at which the armature plate 29 is rotating relatively to the electromagnet. If, however, the armature plate is composed largely .of ironcontainlng a substantialamount up to about by weight 'of silicon, the force-derived from thefelectromagnet as a result of its frictional engagement with the armature plate and applied to the brake shoes is substantially constant over wide ranges 1 of speeds of the armature relatively to the electromagnet.

As pointed out above, these different behaviors of armatures of different compositions appear to be due to the fact that eddy currents are generated in the armature plate during rotationvthereof in contact with the electromagnet. If an ordinary iron or steel armature plate is employed, these eddy currents attain a considerable magnitude and are able to develop in. the armature a magnetic flux of substantial value which opposes the flux produced by the electromagnet itself. If, however, the armature plate is composed of an alloy of iron and a.

which are tolerable force variations in most practical. apparatus, are-not beyond the scope of the expression substantially; constant".

The amount of silicon with which the iron or the armature plate is alloyed should-be substantial in order to obtain satisfactory results. Ordinarily at least about 3% silicon should be employed, and larger amounts may be used with advantage. In 'general'no particular advantage is obtained using more than about 10% by weight of silicon, and 'for most practical purposes an substance such as silicon capable of inhibiting the occurrence of eddy currents, the magnitude of the eddy currents set up in the armature, is significantly reduced and the attraction of the electromagnet to the rotating armature plate is substantially unopposed, in consequence of which a substantially constant force is derived over a considerable range of speeds of the ar" mature plate relatively to the electromagnet' for any given degree of energization of the electromagnet.

The extent to which the force derived from the electromagnet is reduced by an increase in the speed of rotation of the armature, when the Speed of armature-revolution per minute Armature composition Hi h carbon abras on-resistant steel. 69 50 50 45 40 33 27 Copper steel 53 51 47 A4 42 36 A. E. 4050 steel 68 60 55 51 48 45 38 Silicon steel.

4% silicon 70 68 66 63 59 57 6% silicon 63 61 59 58 57 56 55 It will be noted from the foregoing table that in the case of the first three armatures listed the force derived at 800 R. P. M. was about to 60% below the force derived at 100 R. P. M., whereas in the case of the silicon steel armatures the force derived at 800R. P. M. (700 R. P. M. in the case of the 4% silicon steel) was only about 13% to 19% below the force derived at 100 R. P. M. For practical purposes the force derived using the armatures of silicon steel thus can be considered substantially conupper weight of about 8% by weight is adequate. For many purposes an armature plate composed of about 5% by weight of silicon, and the balance substantially all iron, is economical and quite satisfactory.

The armature plate may be composed wholly of the iron-silicon alloy described above, but advantageous results may be obtained by employing an armature plate having a surface portion 39 (Fig. 4) composed of a relatively hard, wearresistant metal and an underlying portion 40 composed substantially of an iron-silicon alloy as described above. The hard wear-resistant surface portion 39 of the armature is suitably configured for engagement with the working faces of the pole pieces of the electromagnet. Being hard and wear-resistant, this surface portion of the I armature plate will stand up well over long periods of time in operating engagement with the electromagnet workingface, and will protect the underlying main body partion 40 of the armature .plate, which is composed of the less wear-resistant silicon-iron alloy, from'injury-due to mechanical causes. The hard wear-resistant surface portion 39 of the armature plate should be relatively thin, so as to interfere as little as possible with the magnetic quality of the armature plate as a whole,

resistant surface portion of the order of 0.020

stant over the range of armature speeds given.

ly constant over a considerable range of speed of armature relatively to electromagnet, variations in the force of the orderof 15% occurring over a variation in speed of the order of 800%, I

and yet should be thick enough so as to protect the underlying portion of the armature. A wearinchin thickness generally is amply thick. The main body portion 40 of the armature is of substantial thickness, the actual dimension being dependent upon the particular design of the electromagnet'with' which it is intended to operate.

Composite armature plates of the character described may be prepared by welding a thin sheet of a 'case-hardenable steel to a relatively thick sheet of a suitable silicon-iron alloy. The two" sheets should, of course, be securely bonded together both for mechanical strength and to elim inate the occurrence of undesirable air gaps in the magnetic circuit.

An advantageous feature of armature plates composed of silicon steel is their ability to resist abrasion, scoring, chipping, and other detrimental effects resulting from heavy rubbing pressure in contact with the electromagnet when the latter isenergized. Many steels, when subjected to the service imposed on armature plates in apparatus of the character described above, are badly scored or chipped after a short periodof time. Scoring or chipping adversely affects proper functioning of the armature plate to a serious extent. Silicon steel has been found to resist scoring, chipping, and other objectionable types of defacing, and for this reason also may be used with advantage in the armature plate of electromagnetic apparatus ofthe character described. Ordinary silicon steel such as that described above possesses adequate resistance to abrasion, scoring, chipping, and the like for many purposes, but this resistance may be enhanced by constructing the armature plate, as described heretofore been used chiefly in the form of very thin sheets in laminated cores for electrical apparatus, particularly radio transformers.

Although particular reference has been' made above to silicon steel for use in armature plates according to the invention, it is understood that gization of the electromagnet is substantially constant over a considerable range of speedof the armature relatively to the electromagnet.

4. Apparatus of the character described comprising an electromagnet, means for energizing the electromagnet, and a generally disc-shaped armature mounted for rotation relatively to the e the amount of silicon present in'the armature being sufficient so that the force derived at a the term silicon steel as used herein is intended to include other equivalent magnetic metals or alloys in which the development of eddy currents is inhibited and which otherwise possess the advantageous characteristics of silicon stee itself.

Although the invention has been described above with particular reference to the embodiment of electromagnetic apparatus in accordance with the invention in an internal shoe brake, it

is understood thatthe invention is equally applicable to other types of electromagnetically operated brakes, such as external brakes and disc brakes, and to other types of equipment, such as clutches, in which the electromagnetic apparatus may be employed as the operating or control mechanism.

I claim:

1. Apparatus for deriving force by magnetically induced friction comprising an electromagnet, means for energizing the electromagnet, and an armature mounted for movement relatively to the electromagnet and so arranged that upon energization of the electromagnet during movement of the armature relatively thereto a frictional force is produced between the armature and the electromagnet, said armature comprising a metallic member composed largely of iron and containing silicon in sufficient amount so that the force derived at a given degree of energization of -the electromagnet is substantially constant over a considerable range of speed of the armature relatively to the electromagnet.

2. Apparatus for deriving force by magneti cally induced. friction comprising an electromagnet, means for energizing the electromagnet, and an armature mounted for movement relatively to the electromagnet and so arranged that upon energization of the electromagnet during movement of the armature relatively thereto a frictional force is produced between the armature and the electromagnet, said armature comprising a metallic member composed largely of iron and containing a substantial amount up to about 10% by weight of silicon, the amount of silicon present in the armature being sufficient so that the force derived at a given degree of energization of the electromagnet is substantially constant over a considerable range of speed of the armature relatively to the electromagnet.

3. Apparatus of the character described comprising an electromagnet, means for energizing ;the electromagnet, and an armature mounted for relative movement in magnetic relation and frictional engagement with said electromagnet, said armature being composed largely of iron and containing silicon in sufficient amount so that the force derived at a given degree of energiven degree of nergization of the electromagnet is substantially constant over 'a considerable range of speed of the armature relatively to the electromagnet.

5. Apparatus of the character described comprising an armature, an electromagnet mounted with its pole pieces normally in light-pressure contact with the armature, means for controllably energizing the-electromagnet to produce relatively heavy-pressure contact between said armature and electromagnet, and means for moving-the armature relatively to the electromagnet, said armature being composed largely of iron and containing silicon in suflicient amount so that the force derived at a given degree of energization of the electromagnet is substantially constant over a considerable range of speed of the armature relatively to the electromagnet.

6. Apparatus of the character described comprising a generally disc-shaped armature mounted for rotation about its axis, an electromagnet mounted with its pole pieces normally in light-pressure contact with the armature, and

means for controllably energizing the electromagnet to produce relatively heavy-pressure contact between said armature and electromagnet, said armature being composed largely of iron and containing from about 3% to about 8% by weight of silicon.

7,. Apparatus of the character described comprising an armature, an electromagnet mounted with its pole pieces normally in light-pressure contact with the armature, means for controllably energizing the electromagnet to produce relatively heavy-pressure contact between said armature and electromagnet, and means for moving the armature relatively to the electromagnet, said armature having a surface ,portion in contact with-the electromagnetcomposed of a relatively hard, wear-resistant metallic composition and an underlying portion composed largely of iron containing silicon in suflicient amount so that the force derived at a given degree of energization of the electromagnet is substantially constant over a considerable range of speed of the armature relatively to the electromagnet.

8. Apparatus of the character described comprising a generally disc-shaped armature mounted for rotation about its axis, an electromagnet mounted with-its pole pieces normally in lightpressure contact with the armature, and means for controllably'energizing the electromagnet to produce relatively heavy-pressure contact between said armature and electromagnet, said armature having a surface portion in contact with the electromagnet composed of a relatively hard, wear-resistant ferrous composition securely bonded to an underlying portion composed largely 9. An electromagnetic brake comprising a backmg plate, an electromagnet supported from said backing plate, a rotatable brake drum, an armature mounted for rotation with said drum in light-pressure contact with the pole pieces of said electromagnet, means for controllably energizing the electromagnet, and brake shoes arranged to be actuated by said electromagnet upon energization thereof during rotation of the armature, said armature being composed largely of iron and containing silicon in suflicient amount so that the force with which the brake shoes are actuated at a given degree of energization of the electromagnet is substantiallyconstant over a considerable range of speed of the armature relatively to the electromagnet.

10. An electromagnetic brake comprising a backing plate, an electromagnet supported from said backing plate, a rotatable brake drum, an

armature mounted for rotation with said drum in light-pressure contact with the pole pieces of said electromagnet, means for energizing the electromagnet, and brake shoes arranged to be actuated by said electromagnet upon energization thereof during rotation of the armature, said armature having a surface portion in contact with the electromagnet composed of a relatively hard, wear-resistant ferrous composition securely bonded to an underlying portion composed large- 1y of iron containing silicon in sumcient amount the metal at and adjacent said surface being of a relatively hard, wear-resistant metallic composition, and the metal underlying said hard,

twear-resistant surface portion being composed largely of iron and containing silicon in suffl- 'cient amount so that the force derived at a given degree of energization of the electromagnet is substantially constant over a considerable range of speed of the armature relatively to the electromagnet.

12. An armature plate adapted for use in apparatus of the character described comprising a relatively thin, generally disc-shaped member having a surface portion composed of a relatively hard, wear-resistant ferrous composition adapted to engage with the pole pieces of an electromag- -net, said surface portion being securely bonded to an underlying portion composed largely of iron and containing from about 3% to about 8% by weight of silicon.

- HARRY W. PHAIR. 

